An insurance company has three types of annuity products: indexed annuity, fixed annuity, and variable annuity. You are given:
i. In a year, 7,000 customers purchase indexed annuity, 5,000 customers purchase the fixed annuity, and 6,000 customers purchase the variable annuity.
ii. The number of customers who purchase both indexed annuity and fixed annuity, but not variable annuity is 1,200.
iii. The number of customers who purchase both indexed annuity and fixed annuity is 500 more than the number of customers who purchase both fixed annuity and variable annuity.
iv. One-fourth of the customers who purchase both indexed annuity and variable annuity also purchase fixed annuity.
v. 3,800 customers purchase only the indexed annuity.
Determine the number of customers who purchase only one annuity product.